Preparation of ethylenically unsaturated hydrocarbons with low acetylenic content



United States Patent 3,476,824 PREPARATION OF ETHYLENICALLY UNSATU-RATED HYDROCARBONS WITH LOW ACETY- LENIC CONTENT Marvin Z. Woskow,Houston, Tex., assignor to Petra-Tex Chemical Corporation, Houston,Tex., a corporation of Delaware No Drawing. Filed Sept. 20, 1966, Ser.No. 580,578 Int. Cl. C07c 5/18; C07b 3/00 US. Cl. 260-680 9 ClaimsABSTRACT OF THE DISCLOSURE Method for dehydrogenation of hydrocarboncompounds to form ethylenically unsaturated hydrocarbons of lowacetylenic content characterized by contacting the hydrocarbon in afirst zone with oxygen and specified iron containing catalysts at atemperature of at least 600 F., and then feeding the reaction productfrom this first zone at a temperature of at least 800 F. into a secondzone containing an alkalized iron oxide catalyst to produce theethylenically unsaturated hydrocarbon product of low acetylenic content.

This application relates to a process for the production ofethylenically unsaturated hydrocarbons.

Unsaturated hydrocarbon compounds such as styrene, butene, butadiene,isoprene and the like are produced by the catalytic dehydrogenation ofmore saturated compounds. Improved processes have recently beendeveloped whereby higher conversions, yields and selectivities ofproducts are obtained by the dehydrogenation in the presence of oxygenand suitably a halogen. These processes are referred to as oxidativedehydrogenations.

One difiiculty in these processes is that the reactor eflluent containsacetylenes such as vinyl acetylene and methyl acetylene. Whileacetylenes may be present in a relatively small percentage, theyinterfere with the subsequent use of the unsaturated product and theirremoval has been the subject of considerable research effort. US. Patent2,969,407 describes a process for the selective removal of acetyleneswherein the acetylene containing mixture is passed over an alkalizediron oxide catalyst at elevated temperatures with the resultantdestruction of the acetylenes. However, such a process requires theaddition of substantial quantities of heat in the form of steam. Afurther disadvantage is that the ethylenically unsaturated hydrocarbontends to be destroyed by such a process.

It is therefore an object of this invention to provide an economicalprocess for the production of high yields of ethylenically unsaturatedhydrocarbons which contain only low concentrations of acetyleniccompounds.

According to this invention these and other objects may be accomplishedby a process comprising contacting a hydrocarbon to be dehydrogenatedwith free oxygen at a temperature of at least 600 F and in the presenceof a catalyst comprising oxygen, iron and at least one element otherthan iron selected from the group consisting of metals of Periodic TableGroups 211, 2b, manganese, cobalt, nickel or mixtures thereof, feedingthe reaction product from the said first zone at a temperature of atleast 800 F. to a second zone comprising an alkalized iron oxidecatalyst to produce the said ethylenically unsaturated hydrocarbonproduct.

The hydrocarbon composition to be fed to the first zone will preferablyhave from 2 to 8 carbon atoms such as propane, propylene, methylacetylene, n-butane, isobutane, n-butene-l, n-butene-2, butadiene-l,3,vinyl acetylene, n-pentane, isopentane, n-pentene-l, n-pentene-3,476,824 Patented Nov. 4, 1969 2, ethyl benzene, cyclohexane andmixtures thereof. Excellent results may be obtained with acyclichydrocarbons of 3 to 5 carbon atoms, and particularily hydrocarbons of 4to 5 carbon atoms having a straight chain or at least 4 carbon atoms.

A preferred feature of this invention comprises a process for theproduction of high purity diolefins from a hydrocarbon stream containingimpure monoolefin and diolefin mixtures. This hydrocarbon stream maycontain hydrocarbon acetylene compounds such as vinyl acetylene andmethyl acetylene as impurities. According to this embodiment of theinvention, the hydrocarbon mixture is fed to a fractional distillationzone wherein diolefin is taken overhead. At the same time, a higherboiling fraction containing monoolefin as the major component is takenoif at a lower point in the distillation zone. For example, thedistillation zone may consist of a fractional distillation column. Anytype of conventional fractional distillation column may be employed suchas tray or plate type columns. The monoolefin rich mixture to be furtherprocessed may be either taken oif as the bottoms from the distillationcolumn or as a side stream from the distillation column. The monoolefinrich mixture may then be fed to the first and second zones as describedabove wherein in the first zone the mixture is contacted with a catalystcomprising oxygen, iron and at least one of the defined elements. In thesecond zone the composition is contacted with the alkalized iron oxidecatalyst as described above. The eflluent from the second zone containsthe diolefin product of high purity. This unsaturated product of highpurity may then be combined either directly or indirectly with theoverhead from the fractional distillation zone. An example of anindirect combination of the overhead would be a process wherein theproduct of the second zone is recycled upstream in a purificationsequence such as to the feed to a cuprous ammonium acetate or otherpurification step. Furthermore, a portion of the product may be recycledto the said fractional distillation zone. The preferred hydrocarbonmixture to be fed to the fractional distillation zone will containn-butene, methyl pentene, isoprene or mixtures thereof as the majorcomponents. Particularly preferred is a composition containing a mixtureof nbutene, vinyl acetylene, and butadiene-l,3 as the major components.

The catalyst in the first zone will comprise iron, oxygen and as asecond component at least one element selected from the group consistingof metals of Periodic Table Groups 2a, 2b, manganese, cobalt, nickel ormixtures thereof. The preferred elements in Groups 2a, are Mg, Ca, Srand Ba, with Mg being particularily preferred. The preferred elements inGroup 2b are Zn and Cd. The Periodic Table referred to may be found e.g.on the back cover of the 45th Edition 1964-5 of the Handbook ofChemistry and Physics (Chemical Rubber Company, Cleveland, Ohio). Thus apreferred group of elements is Mg, Ca, Sr, Ba, Mn, Co, Ni, Zn, Cd andmixtures thereof. The catalyst will have iron in the catalyst surface inan amount from 20 to 95, and preferably from 30 to weight percent of thetotal weight of iron and the second metallic element(s). The catalystwill comprise oxygen, and excellent results have been obtained when thedefined elements are present in a crystalline structure. The bestresults have been obtained when the catalysts comprise ferrites.Examples of these catalysts are disclosed e.g. in Belgium Patent 657,827issued June 30, 1965, which disclosure is herein incorporated byreference. Free oxygen must be present in the first zone. The quantityof oxygen will normally be present in an amount of at least 0.2 mols permol of hydrocarbon compound fed to the zone. A usual range is from 0.1to

2.5 mols of oxygen per mol of hydrocarbon compound and a preferred rangeis from 0.2 to 2.0 mols per mol. The oxygen may be present as such, oras air, as air enriched with oxygen, or the oxygen may be diluted withdiluents such as nitrogen, helium, argon and the like. The oxygen may beintroduced in any manner to the dehydrogenation zone.

The halogens employed, if any, will preferably be iodine, bromine orchlorine, and the form of the halogens may be the halogens themselves orany halogencontaining materials which liberate free halogen under theconditions of the reaction as defined hereinafter. For example,chlorine, bromine and iodine; hydrogen chloride, hydrogen bromide andhydrogen iodide; the alkyl halides such as alkyl iodides and bromideswherein the alkyl groups preferably contain 1 to 6 carbon atoms;ammonium halides including ammonium chloride, ammonium bromide, ammoniumiodide and ammonium fluoride; and mixtures of these may also beemployed. The halogens,

hydrogen halides, ammonium halides and alkyl halides wherein the alkylgroups contain 1 to carbon atoms, have been found to be particularlyuseful in the practice of this invention. Any suitable combination ofreactants may be used as chlorine and hydrogen bromide; chlorine andbromine; hydrogen chloride and bromine; chlorine and hydrogen iodide,bromine and iodine and the like added together or separately.

The total amount of halogen used may be varied quite widely, usually anamount greater than 0.001 mol of halogen per mol of hydrocarbon compoundto be dehydrogenated. More usually, at least about 0.005 mol of totalhalogens per mol of hydrocarbon compound will be employed. Large amountsof halogens may be used, as high as one-half to one mol or more per molof hydrocarbon compound to be dehydrogenated if desired, but generallyonly very small amounts of halogens are used, normally less than about0.2 mol total of halogens, per mol of organic compound to bedehydrogenated. The first zone may be a fixed or fluid bed reactor.Reactors such as those conventionally used for the dehydrogenation ofhydrocarbons may be employed. The total pressure in the first zone maysuitably be about atmospheric pressure. However, higher pressures orvacuum may be used. Pressures such as from about atmospheric (or below)up to about 100 to 200 p.s.i.g. may be employed. The first zone reactionwill normally be conducted at a temperature of reaction between about600 F. to about 1500 F. or higher although generally the maximumtemperature in the reactor will be within the range of about 700 F. and

1300 F. The flow rates of the reactants may be varied quite widely andwill be dependent somewhat on whether fixed or fluid bed reactor isemployed. Good results have been obtained with flow rates of thehydrocarbon feed ranging from about A to liquid volumes of hydrocarbonfed per volume of the first zone per hour, with the volumes ofhydrocarbon being calculated as the equivalent amount of liquidhydrocarbons at standard conditions of 15.6 C. and 760 millimeters ofmercury absolute. For the purpose of calculating flow rates the firstzone is defined as the portion of the first zone which contains catalystand which is at a temperature of at least 600 F. In other words, thevolume of the first zone is equivalent to the volume of the catalystzone if it were empty. The residence or contact time of the reactants inreaction. Contact times such as about 0.001 to about 5, 10 or 25 secondshave been found to give excellent results. Under certain conditions,higher contact times may be utilized. Contact time is the calculateddwell time of the reaction mixture in the reaction zone assuming themols of product mixture are equivalent to the mols of feed.

The second zone contains an alkalized iron oxide catalyst. Thesecatalysts suitably contain iron oxide as the major component togetherwith an alkali metal. These catalysts are disclosed e.g. in Davies etal. US. Patent 2,461,147, issued Feb. 8, 1949, which disclosure isherein incorporated by reference. The catalyst may also contain chromiumoxide. 'Suitable catalysts will contain alkali (preferably potassium) inan amount of at least 5 mol percent alkali, (preferably about 5 to 50mol percent alkali) calculated as Me O (Me being the alkali metal) basedon the iron oxide, calculated as Fe O Stabilizers such as chromium maybe present such as from about 2 to 20 mol percent (calculated as Me Oe.g. Cr O based on the iron oxide).

The temperature in the second zone should be maintained at least 800 F.and preferably the maximum temperature in the zone will be between about800 F. and 1150 F. It is preferred that the temperature be maintainedbetween 1000 F. and 1150" F. Good results are obtained at temperaturesbetween 1040 F. and 1070 F. and exceptionally good results are obtainedat temperatures between 1070 F. and 1150 F. It will be noted that theuse of the combination catalyst-permits the utilization of highertemperatures and thus greater efficiency in the process.

The flow rates in the second zone will be within the same ranges asthose of the first zone.

The following examples describe my invention in greater detail; however,it is to be understood that the examples are for illustrative purposesonly and the invention is not limited thereto.

EXAMPLE 1 A one-inch reactor tube is loaded with catalysts as follows:the bottom six inches of the tube (second zone) is filled with W pelletsof a catalyst having 67% Fe O 3% Cr O and 30% KOH (all parts by weight);the middle ten inches of the tube is filled with vycor chips to separatethe actives, and the top 4 inches of the tube (first zone) is filledwith magnesium ferrite. A hydrocarbon stream containing, by mol percent,30.9% trans butene-Z, 46% cis-butene-2, 6.1% vinylac'etylene and 16.9%butadiene was fed into the top of the reaction tube. Reaction conditionswere held at 0.5 liquid hourly space velocity (LHSV) over the totalreactor area, 0.25 mols oxygen per mol hydrocarbon, and 15 mols steamper mol hydrocarbon. The inlet temperature to the first zone is 715 F.Reaction temperature in the second zone is approximately 1075 F. Theeffluent from the second zone contained 27.3 mol percent butadiene and0.4 mol percent vinylacetylene.

EXAMPLES 2 TO 4 The general procedure of Example 1 is repeated usingdifferent hydrocarbon feeds and reaction conditions. The

the first zone depends on several factors involved in the results areShown in the table- The Oxygen is fed as ail TABLE Feed (M01 percent)Product (M01 percent) Vinyl Flow Temperature, F. Vinyl Buta- Aoetn- RateSteam Buta- Acetdiene Butene-2 Butene-l ylene Butane LHSV (Mols) InletMax. OQIHebn dlene ylene Butene Exam 1e 2--.- 23. 2 70. 2 0. 7 5. 6 0. 30.5 15 710 1, 070 0. 25 39. 4 0. 3 55. 7 Examglo 3- 0. 9 08. 0 0. 8 1. 30. 5 15 725 1, 0. 25 23. 0 0.03 74. Example 4 13. 7 81.0 0. 5 4. 7 0.10. 5 14 717 1, 085 0.25 30.1 0. 2 65. 0

EXAMPLE 5 A mixture of n-butane and butene is dehydrogenated in thepresence of oxygen, ammonium bromide and oxygen to form a reactionefiluent. The efiluent is condensed, compressed and purified to form a Chydrocarbon mixture which is then fractionally distilled in a traytower. The bottoms from the tower are fed to the process of Example 1above and the efiluent from the two zone reactor is combined with theoverhead from the fractional distillation tower to provide butadiene-1,3of high purity containing less than 0.5% vinylacetylene.

I claim:

1. A method for the dehydrogenation of hydrocarbon compounds selectedfrom the group consisting of nbutane, n-butene, methyl pentane, methylpentene and mixtures thereof to form ethylenically unsaturatedhydrocarbons of low actylenic content comprising contacting in a firstzone the hydrocarbon to be dehydrogenated with free oxygen at atemperature of at least 600 F. and in the presence of a catalystcomprising iron, oxygen, and at least one element selected from thegroup consisting of metals of Periodic Table Groups 2a, 2b, manganese,cobalt, nickel and mixtures thereof, directly feeding the reactionproduct from the said first zone at a temperature of at least 800 F. toa second zone comprising an alkalized iron oxide catalyst containing atleast 5 mol percent alkali calculated as Me O (Me being the alkalimetal) based on the iron oxide to produce the said ethylenicallyunsaturated hydrocarbon product of low acetylenic content.

2. The method of claim 1 wherein the catalyst in the first zonecomprises a ferrite.

3. The method of claim 1 wherein the catalyst in the said first zonecomprises magnesium ferrite.

4. The method of claim 1 wherein the catalyst in the second zonecomprises an alkalized iron oxide catalyst containing chromium.

5. The method of claim 1 wherein the hydrocarbons to be dehydrogenatedcomprises n-butene and the said hydrocarbon product is butadiene-1,3 oflow vinylacetylene content.

6. The method of claim 1 wherein the temperature in the said second Zoneis between 1040 F. and 1150 F.

7. The method of claim 1 wherein the temperature in the said second zoneis between 1070 F. and 1150 F.

8. A method for preparing high purity diolefin selected from the groupconsisting of butadiene-1,3, isoprene and mixtures thereof from ahydrocarbon mixture containing the said diolefin and the correspondingmonoolefin of the same number of carbon atoms which comprisesfractionally distilling in a fractional distillation zone the saidmixture to take off overhead the diolefin and at the same time takingoff a monoolefin rich mixture from a lower portion of the distillationzone, contacting in a first zone the said monoolefin rich compositionwith free oxygen at a temperature of at least 600 F. and in the presenceof a catalyst comprising in a crystalline structure oxygen, iron and atleast one element selected from the group consisting of metals of thePeriodic Table Groups 2a, 2b, manganese, cobalt, nickel, and mixturesthereof, directly feeding the reaction product from the said first zoneat a temperature of at least 800 F. to a second zone containing analkalized iron oxide catalyst containing at least 5 mol percent alkalicalculated as Me 0 (Me being the alkali metal) based on the iron oxideto produce the said diolefin of high purity.

9. The method of claim 8 wherein the monoolefin is nbutene and thediolefin is butadiene-1,3.

References Cited UNITED STATES PATENTS 2,969,407 1/1961 Rosenberg et al.260--68l.5 3,284,536 11/1966 Bajars et al. 3,308,181 3/ 1967 Pitzer.

PAUL M. COUGHLAN, JR., Primary Examiner

